A238768 - OEIS

%I #7 Feb 24 2018 09:25:34

%S 3,6,14,32,72,164,372,844,1916,4348,9868,22396,50828,115356,261804,

%T 594172,1348492,3060444,6945772,15763644,35776076,81194908,184274348,

%U 418216316,949154828,2154136156,4888878444,11095460412,25181489612

%N Number of n X 1 0..3 arrays with no element equal to the sum modulo 4 of elements to its left or elements above it.

%C Column 1 of A238775.

%H R. H. Hardin, <a href="/A238768/b238768.txt">Table of n, a(n) for n = 1..210</a>

%F Empirical: a(n) = a(n-1) + 2*a(n-2) + 2*a(n-3).

%F Empirical g.f.: x*(3 + 3*x + 2*x^2) / (1 - x - 2*x^2 - 2*x^3). - _Colin Barker_, Feb 24 2018

%e Some solutions for n=5:

%e ..3....3....2....1....1....2....1....3....2....1....3....3....1....1....2....1

%e ..1....1....3....2....2....3....3....2....3....3....1....2....2....2....1....3

%e ..2....2....3....1....2....3....1....2....2....3....2....3....2....2....2....2

%e ..1....3....1....3....3....3....2....2....2....2....1....1....3....2....2....1

%e ..1....3....3....2....1....1....2....2....2....2....2....2....3....1....2....2

%Y Cf. A238775.

%K nonn

%O 1,1

%A _R. H. Hardin_, Mar 05 2014